A plasma torch generates an electrical discharge referred to as a pilot arc between an electrode and a nozzle inside a torch, moves the pilot arc, and establishes a plasma arc, which is an electrical discharge between a workpiece and an electrode for cutting the workpiece, when cutting or other work is started. An electroconductive path for generating the pilot arc extends inside the torch from the torch main unit to the nozzle.
A typical example of a conventional structure of an electroconductive path is disclosed in Japanese Laid-open Patent Application No. 11-221675, in which a cap (referred to as an inner cap in the publication) is used for mounting the nozzle on the torch main unit. The nozzle is held at the distal end of the inner cap, and the base end of the inner cap is threaded onto the torch main unit. The distal end of the inner cap has a metal surface that is in direct contact with the nozzle. Such an inner cap and screw of the torch main unit form an electroconductive path that extends from the torch main unit to the nozzle.
Japanese Laid-open Patent Application No. 2000-334570 discloses a plasma torch in which an electroconductive path having a different structure than that described above is used. In this torch, a cap (referred to in the publication as a retaining cap) for mounting the nozzle on the torch main unit is electrically insulated from the nozzle and does not form an electroconductive path. The electroconductive path is formed instead by a nozzle seat made of metal inside the torch main unit. When the nozzle is mounted on the torch main unit with the aid of the retaining cap, the base end surface of the nozzle is pressed against and makes contact with the distal end surface of the nozzle seat to form an electrical connection between the nozzle and the nozzle seat. Furthermore, a plurality of elastic electrical connection terminals provided to the front end part of the nozzle seat makes contact with the external surface of the base end of the nozzle by way of a strong elastic force directed toward the center of the nozzle. The electrical connection terminals sandwich the nozzle from the outside and an electrical connection is formed between the nozzle and the nozzle seat.